DE23 skeg length

Power Boats only. Please include the boat type in your question.
Stevann
Frequent Poster
Frequent Poster
Posts: 15
Joined: Wed Jan 15, 2020 10:17 pm
Location: Blenheim New Zealand

DE23 skeg length

Post by Stevann »

Hello from NZ.
Im 2/3 through a DE23 build with Hull and Topsides near complete. I had an outboard mechanic call today to use his jig to drill the outboard mount holes in transom before glassing the well.
He was surprised the skeg came back to transom and recommended cutting it back 3ft to avoid cavitation?
Any thoughts from experienced builders?

I'm fitting a ETEC 75HP. Does anyone have similar HP fitted? I'm interested in gauging what performance might be achieved?

Thank in advance.

Steve A

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: DE23 skeg length

Post by fallguy1000 »

He is right!

You want clean flow without air bubbles going to the prop for efficiency and to the water intake for cooling.

Noone here argues the other way; fyi.
My boat build is here -------->

viewtopic.php?f=12&t=62495

User avatar
cape man
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8269
Joined: Sun Jan 20, 2008 12:02 pm
Location: Lithia, Florida

Re: DE23 skeg length

Post by cape man »

You do want clean water coming off the transom, but 3 feet seems a bit much for the required setback. I have a 1 inch tall skeg on the bottom of my dory with a yamaha 70 hp. The skeg stops 18 inches from the transom. I have not had any cavitation issues and my performance is fine. How big is your skeg?
The world always seems brighter when you've just made something that wasn't there before - Neil Gaiman

User avatar
cape man
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 8269
Joined: Sun Jan 20, 2008 12:02 pm
Location: Lithia, Florida

Re: DE23 skeg length

Post by cape man »

I found this from another builder's thread. Looks like almost 2 feet back and the skeg transitions down before that.

Image
The world always seems brighter when you've just made something that wasn't there before - Neil Gaiman

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: DE23 skeg length

Post by TomW1 »

I usually recommend 2' minimum on large high-speed boats. The higher the speed the more clearance you need in front of the propellor. 2' should work fine for the DE23 and a 75HP.

Looking at the study plans the 75HP you have planned will give you a top speed in the low 30's mph. Jacques numbers were with a 70HP motor. I can run it through my calculators if you want me to, to get a more accurate top speed estimate.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Stevann
Frequent Poster
Frequent Poster
Posts: 15
Joined: Wed Jan 15, 2020 10:17 pm
Location: Blenheim New Zealand

Re: DE23 skeg length

Post by Stevann »

Thank you for your comments.
I really appreciate the experience out there.
Is there any DE23 owners out there that can give their experience?
I wonder why the plans show a full length if that should be?
The boat hull is flipped and near-complete but best I look to modify the skeg before launch day.
Maybe the plans should be changed.
No need for speed calcs, as it was of interest only - I guess the actual speed is dependent on boat weight so it will vary between individual fitouts. I just wondered what owners had found after launching
Happy Days!

Matt Gent
Very Active Poster
Very Active Poster
Posts: 600
Joined: Sat Jan 05, 2008 7:54 am
Location: Treasure Coast, FL

Re: DE23 skeg length

Post by Matt Gent »

On my DE25 the keel runs all the way to the transom. However my engine is mounted on a 30" setback bracket.

When the engine was mounted up very high I did get some slippage in turns, but now that it is lowered I do not.

The anti-broaching moment is greatest at the back end of the keel, and my boat does not want to broach at all.

Inboards run the prop right off the keel. And at 20mph I bet the keel turbulence travels back much more than 2 feet.

Hard to say how detrimental it could be. Pretty easy to trim it later, but I'd be tempted to take 2' off of it now to avoid the sealing and painting later.

Stevann
Frequent Poster
Frequent Poster
Posts: 15
Joined: Wed Jan 15, 2020 10:17 pm
Location: Blenheim New Zealand

Re: DE23 skeg length

Post by Stevann »

Yes Thanks Matt,
I agree easier to do it before final painting.
What HP did you fit and what speed do you get from your DE23?
Steve A

Post Reply

Who is online

Users browsing this forum: Amazon [Bot] and 3 guests